海洋热事件形成机制的初步探讨

High SST has significant influence on the earth's climate systems. In order to investigate the behavior of short-term, large scale, very high SST phenomena, in our previous study,we have detected the hot event (HE) associated with very high SST of around 30℃ using the advance satellite-derived SST. The HE is defined as a connected region with SST > the time-dependent SST threshold of about 30℃, having a minimum areal size greater than 3×10 6 km2 and lasting for a period longer than 10 days. It is strongly suggested that HE was a coupled system of the ocean and atmosphere in the Indo-Pacific warm pool. many studies have tried to understand generation mechanism of a wide area with very high SSTs. Its appearance is relative to clear sky and low wind speed conditions. Previous studies speculated that, when deep convection is suppressed in the warm pool region by remotely forced atmospheric subsidence, the wide area with very high SST (>30 C) can be formed. The remote forcing was supposed to be "remote convection" by Tompkins(2001).Our study will show the observation evidences of "remote convection" for HEs, and reveal the main formation mechanism of HE. Using the advance satellite merged SST data, reveal the statistic features for all HEs in 1993-2012. Based on satellite atmosphere observation data, the remote convections for HEs will be identified. The way of the organization of "remote convection" in the condition of El Ni?o, MJO and summer monsoon will be investigated. Our result will extend our knowledge of tropical air-sea interaction and improve our understanding and forecasting skill for short-term (sub monthly) climate variations.

本研究探讨短期，大范围高海温现象即海洋热事件的形成机制。在我们前期研究中，海洋热事件被定义为海温高于30℃面积大于3×106 km2且持续10天以上的现象。晴空，静风条件下的强烈太阳辐射是海洋热事件发生的重要因素。近年研究推测，这些天气条件与周边海区大气深对流活动所致的局地高层下沉运动有关。本研究项目，将收集热事件及外源对流强迫有关的观测证据，揭示海洋热事件形成的物理机制及气候影响。利用新一代高分辨率多卫星合成海温资料，统计热事件的大量个例，阐述它们的活动特征。基于相关统计数据，分析外源大气对流强迫，通过识别追踪对流云团及大气环流条件，估算对流强迫在热事件中的动力热力贡献。考察热带地区主要气候变动信号(厄尔尼诺、季节内振荡、夏季风等)的活动对外源大气对流强迫的影响情况从而间接影响热事件的形成。研究结果将会拓展对热带海气相互作用的认识，推进对短期气候变动的理解和预测。

本项目通过对不同海区，短期，大范围高海温事件的形成机制做了分析，并对高海温区域强烈的海气相互作用做了深入探讨。我们的研究指出高海温事件形成的共性是有大气深对流系统的遥强迫作用导致大气上层有下沉干燥气流抑制局地对流，有利于形成热事件；而不同的是海洋在不同的海区扮演的角色不同。在ELNINO背景下的秋冬季，赤道中太平洋提供不稳定能量维持2-3天的大气深对流系统的连续产生，从而对赤道西太平洋的大气起遥强迫的作用，促使海温升高形成季节内尺度的热事件。而在孟加拉湾海区（BOB）大气遥强迫的作用主要由季风爆发涡旋和MJO来完成，而海洋障碍层的形成和暖平流的输送也是热事件形成的重要因子。